Furnace

ABSTRACT

A furnace is provided for burning soila organic fuels including highly volatile organic fuels. A combustion chamber with an ash hopper has a slot mouth opening defined by slopes of the walls of the combustion chamber. A burner is disposed beneath the ash hopper mouth opening and extends across its entire width. A bottom blast inlet device generates a turbulent zone in the lower region of the combustion chamber. A duct is further provided for injecting a sulfur-absorbent material into the furnace chamber. The duct is disposed between the burner and the ash chamber and defines a longitudinal axis which traverses the turbulent zone. Preferably, the burner is tilted downwardly and is disposed on a wall in common with the sulfur-absorbent induction duct. The proportion of the sulfur-absorbent materials in the fuel mixture is in the range of 10% to 100% by mass.

FIELD OF THE INVENTION

The invention relates to heat engineering and more particularly, tofurnaces for burning organic fuel. It can be most successfully used forburning solid sulphur-bearing, ie. high-volatile, fuel.

BACKGROUND OF THE INVENTION

As furnaces are designed, a special emphasis is laid on theirenvironmental protection features and specifically, on the furnacesbeing capable of providing combustion regimes that would minimize theamount of furnace compounds vented to the atmosphere.

The nitrogen oxide content of flue gases may be reduced, directly as thefuel is burned, by proper arrangement of the combustion process, i.e.using comparatively simple and economical methods, without the necessityto resort to a complex, bulky and expensive auxiliary equipment. Thus,according to the latest views, a reduced concentration of nitrogenoxides in combustion products may be achieved by an optimum arrangementof three major zones in the flame, namely: ignition andactive-combustion zone, reduction zone and oxidation (reburning) zone.

Known in the art (see USSR Author's Certificate No.483559) is a furnacecomprising a combustion chamber with a burner for supplying the fuel-airmixture mounted on its sidewall. The slopes of the walls in the lowerregion of the combustion chamber define a V-type ash hopper with aslot-like mouth. A bottom blast device formed by, say, an air nozzle isdisposed beneath the ash hopper mouth.

During operation of such furnace, a fuel-air mixture with aless-than-unity excess-air coefficient is supplied through the burner,while from beneath, through the slot mouth, part of the air necessaryfor fuel combustion is supplied by the bottom blast device. As a resultof interaction between two mutually opposing flows, a turbulent zone isformed throughout the lower region of the furnace, whereas aparallel-flow zone is formed in the upper region thereof. An ignitionand active-combustion zone is located adjacent the burner. It is withinthis combustion zone that the bulk of the fine particles of the fuel isburnt out. The medium-sized and coarse particles of the fuel areseparated into the turbulent zone. In the turbulent zone, theseparticles are burnt out in the course of recycling, After burning downto a certain size, they are removed beyond, the turbulent zone andfinally burnt in the upper - parallel-flow - part of the flame. A majorportion of the turbulent zone is characterized by a relative deficiencyin oxygen and serves as a reduction zone, while the oxygen-richparallel-flow zone serves as a reburning zone. In other words, aste-by-step burning of the fuel is conducted in such furnace.

Thus, through the arrangement of the above combustion zones in thefurnace by controlling the supply of the fuel of a particular fractioncomposition and by selecting an appropriate bottom blast rate, a fairlysmall nitrogen oxide content of flue gases may be ensured.

The above mentioned features of a vortex furnace, however, fail toprovide a reduction of the sulphur oxide content of flue gases, since itis virtual impossible to achieve this end using purely aerodynamic andstructural techniques.

Special problems arise when burning high-volatile organic fuels. This isdue to the fact that as such fuel is heated, an excessive amount ofexplosive gases is released in the pulverization system, so that aspecial care is required when selecting the proper scheme of thepulverization process and supplying said fuel to the combustion chamber.Specifically, furnace (inert) gases, rather than air (containing muchoxygen), are generally used for drying such fuels.

Known in the art is a furnace for burning solid organic fuel describedin the book: R. G. Sach “Boiler Plants” Energy, Moscow, 1968, p.77,comprising a prism-shaped furnace chamber with at least one burnermounted on its wall. The furnace is equipped with a fuel chute servingto supply the fuel to a vertical gas-intake shaft. The gas-intake shaftcommunicates at the top through a gas-intake window, by a special duct,with the inner space of the furnace chamber. The gas-intake window isgenerally disposed in the upper region of the furnace chamber. The lowerend of the gas-intake shaft communicates with a pulverizing fan forgrinding the fuel. The pulverizing fan in turn communicates with aburner for supplying fuel to the furnace chamber.

As the furnace is operated, the flue gases from the top of thecombustion chamber are fed through the gas-intake window and the specialduct to the gas-intake shaft in which the fuel supplied from the chuteis predried and otherwise prepared, by the action of the hightemperature of these gases. In this case, there occurs a partial releasefrom the fuel of volatile matter which is mixed with oxygen-deficientinert flue gases. The prepared fuel is transferred to the pulverizerwhere it is ground to the required fineness and then finally dried. Thefuel, along with the gas mixture, is then supplied through the burner tothe furnace chamber wherein it is burned together with the volatilematter that had been released before. Since the release of volatilematter from the fuel, as it is passed through the gas-intake shaft,occurs in the flue gas atmosphere having a relatively smallconcentration of oxygen, no explosive volatile-and-oxygen mixture can beformed under these conditions, thus preventing the risk of explosionsand providing the safety of the fuel pulverization system and thefurnace itself.

This furnace is rather cost-effective, since effluent gases may bepartially used for fuel preparation and drying, and also it may beregarded as environment-friendly, because a complete fuel combustion isensured at comparatively low temperatures, but provided it is alow-sulphur fuel. Otherwise, this furnace would require additionalmeasures to minimize the sulphur oxide content of the exit gases.

Currently, three basic schemes are largely employed to minimize theamount of sulphur in the flue gas: either sulphur is removed from thefuel prior to feeding it to the furnace (generally, at the spot where itis produced), or various calcium- and magnesium-bearing absorbents, suchas lime, calcium carbide etc., are used for cleaning the flue gas beyondthe boiler or, finally these absorbents are immediately injected intothe furnace chamber for direct (dry or semi-dry) binding the sulphur.Besides, there are composite schemes of binding the sulphur contained inorganic fuel. Since calcium compounds belong to low-melting substances,it is essential to feed the absorbent particles to those regions of thefurnace in which the temperature does no exceed the absorbent meltingpoint: otherwise, the absorbent particle surface would be fused with theconsequent clogging of the pores and reduced reaction area . This mightresult in a less economical operation of the furnace due to the slaggingof water walls and even in a complete shutdown of the boiler.

Known in the art is a furnace realizing a method of simultaneous removalof sulphur and nitrogen from the combustion products. The method isdisclosed in the Japanese Patent No. 4-67085.

The furnace comprises a combustion chamber with at least one burnermounted on its wall for supplying the air-fuel mixture. The furnace isprovided with an absorbent-feeding means represening a duct forsupplying the furnace with finely dispersed or slurry-likecalcium-bearing substances for binding sulphur-bearing compounds, whichlies above the burner level on the same wall. In addition, the designprovides a special equipment for recovery of fly ash from the fuelcombustion products, special treatment of this ash and its return to thecombustion zone for recycling.

As such furnace is operated, the air-fuel mixture is supplied to thecombustion chamber through the burner and the sulphur-absorbing agent isconveyed through an appropriate duct. The absorbent is received by thecombustion chamber at a temperature within the range of 900 to 1200° C.In close proximity to the absorbent-feeding duct, a sulphur-bindingreaction occurs. The gaseous combustion products then enter the smokeflue with a special device provided therein for the recovery of fly ash,followed by adding acid to part of the ash recovered to neutralize theunreacted calcium oxide or carbonate, and this ash then goes to waste.Ammonium or urea (or its compounds) is added to the remaining part ofthe ash and the ash is returned to the furnace, to a region withtemperatures ranging from 500 to 1000 ° disposed at the outlet of thecombustion chamber (already beyond its limits). In this region, anadditional simultaneous binding of sulphur and, partially nitrogen (outof oxides) occurs.

In this furnace, combustion is carried out within the parallel-flowzone, which accounts for a relatively small residence time of the fueland absorbent particles within the combustion chamber and hence, a shorttime of interaction between the absorbent and the flue gases. In theseconditions, an effective binding of sulphur is only possible if both thefuel and the absorbent have been subjected to a thorough preparation andits uniform, finely dispersed, structure ensured. Again, the thoroughpulverization of the absorbent is also required to obtain its maximumsurface area and hence, its full utilization, because thesulphur-binding reaction takes place, largely, on the surface. For suchreaction to proceed over the entire surface of an absorbent particletakes more time than the period during which the particle stays within atemperature zone most favourable in terms of the sulphur-bindingreaction conditions, namely: 600 . . . 1100° C. Furthermore, in thepresence of coarse particles of both the fuel and the absorbent, theseparticles will not be carried from the furnace entrained in the flue gasbut will rather fall through the mouth at the bottom of the combustionchamber and be removed along with the slag, with the consequentlyimpaired economical and environmental-control performance of suchfurnace. Even a thorough preparation of the absorbing material, however,fails to provide such degree of pulverization that all the absorbentparticles react to the full with the sulphur oxides. There always is acertain amount of relatively coarser particles having a layer of reactedabsorbent formed on their surface, while the core portion does not takepart in the sulphur-binding reaction. This leads to an increasedconsumption of the expensive absorbent and a lower economical andecological performance of the furnace. In addition, a complicated systemof the post-cleaning of gases after the boiler also results in higherproduction costs.

DISCLOSURE OF THE INVENTION

The aim of the present invention is to provide a furnace design suchthat it allows the use of a sulphur-absorbing material and a fuel ofcomparatively large-sized fraction composition, thereby reducing theexpenses for their preparation, and an essentially complete utilizationof the absorbent at an optimum temperature to permit the binding ofsulphur oxide compounds, thus improving the cost-effectiveness andenvironmental control of the furnace and further, when using ahigh-volatile sulphur-bearing fuel, such design as to provide a safeconcentration of volatile matter within the combustion chamber andhence, a more reliable furnace.

This aim is achieved by providing that in a furnace for burning solidorganic fuel comprising a prism-shaped combustion chamber with an ashhopper having a slot mouth defined by the sloping walls in the lowerregion of the combustion chamber, at least one burner mounted on itswall, and a duct for injecting a sulphur absorbing agent into thefurnace chamber, according to the invention, a bottom blast inlet deviceis disposed beneath the mouth of the ash hopper across its entire widthfor generation of a turbulent zone in the lower region of the combustionchamber, the absorbent is supplied to the furnace chamber mixed with thefuel, and the absorbent-injection duct is disposed at an elevation notabove the burner and so directed that its longitudinal axis traversesthe turbulent zone.

By virtue of the bottom blast inlet means being disposed over the entirewidth of the ash hopper mouth, a turbulent zone is generated in thelower region of the combustion chamber as a result of interactionbetween two opposing streams, i.e. the air-fuel mixture from thedownward-tilting burner and air from the bottom blast nozzle extendingalong the slope of the ash hopper. Owing to the arrangement of theabsorbent-injection duct not above the burner level and due to itsdirection as hereinbefore mentioned, both the fuel and the absorbent aresupplied to the turbulent zone. In the turbulent zones, both thesestreams are mixed and favourable sulphur-binding conditions arise. Bysupplying the absorbent mixed with the fuel, a uniform distribution ofthe absorbent particles throughout the turbulent zone is achieved.

Relatively low temperatures (about 1000° C.) present in the turbulentzone provide, in the first place, optimum conditions for binding thesulphur, since at these temperatures, the rate of the direct reactionbetween calcium oxide and sulphur dioxide exceeds the reverse calciumsulphate decomposition reaction rate. Secondly, no fusion of theabsorbent particle surfaces occurs and consequently, no clogging of thepores and reduction of the reaction surface is observed. A calciumsulphate layer formed on the surface of an absorbent particle andcontinually growing with time remains unfused and porous, enabling thesulphur oxide to penetrate along the cracks and pores and find its wayto the so-far unreacted surface of the absorbent. Thirdly, due torecycling the particles in the turbulent zone, there is a sharp increasein the residence time of particles within the favourable temperaturezone and consequently, in the reaction time and the degree of bindingthe sulphur.

A possible fusion of absorbent particles may only occur as they areconveyed from the turbulent zone to the parallel-flow (high temperature)one of the furnace. In this design, however the sulphur oxide bindingeffect is not much influenced by this circumstance since, firstly, theabsorbent particles have already “done the job” in the turbulent zone,and it is not the active calcium oxide layer that may be fused, butrather a layer of the reaction product, i.e. calcium sulphate. Secondly,the residence time of an absorbent particle within the unfavourable,i.e. parallel-flow, zone is much shorter than the residence time withinthe favourable turbulent zone.

It goes without saying that the coarse particles of the absorbent reactthe longest and the coarse particles of the fuel burn the slowest. Inthe proposed device, however, the largest pieces both of the fuel andthe absorbent are separated into the lower region of the combustionchamber, where they are entrained in the air stream leaving the bottomblast nozzle and are returned to the turbulent zone. Thus theirresidence time within the favourable temperature zone is sharplyincreased. Moreover, the residence time of the fuel and absorbentparticles within the turbulent zone and hence, the sulphur absorptionreaction time may be controlled, depending on the fuel characteristics,by decreasing or increasing the bottom blast rate.

It will be noted that in the proposed furnace, due to the presence of aturbulent zone, the nitrogen oxide content of flue gases is reduced,similarly to what was described above in connection with the knowndevice.

The burner for supplying the air-fuel mixture may be tilted downwards,the absorbent-injection duct disposed on the same wall as the burner anddirected in such a manner as to ensure that the angle formed by thelongitudinal axis of the absorbent-injection duct and a projection ofthis axis onto this wall is no less than the angle formed by the slopedwall of the combustion chamber and a vertical line lying on this wall,and no greater than the angle formed by the longitudinal axis of theburner and a projection of this axis onto the same wall of thecombustion chamber. In this case, the stream of the absorbent suppliedto the combustion chamber is received, predominantly, by the centralportion of the turbulent zone, thereby providing the most thoroughmixing of the absorbent and the fuel and their most effectiveinteraction.

The absorbent-injection duct may be located in the outlet nozzle of thebotton blast device, whereby the furnace design is somewhat simplified.

The proportion of the absorbent in the mixture may range from 10 to 100%by mass, depending on the sulphur content of the fuel.

The furnace may further include a gas-intake shaft, a duct for supplyingthe absorbent to the gas-intake shaft, and a pulverizing fan, allcommunicating with one another, the pulverizing fan communicating inturn with the burner, the duct for injection of the absorbent into thefurnace chamber being aligned with said burner.

In this case, the sulphur-compound binding absorbent is supplied via aspecial absorbent-injectlon duct to the upper region of the gas-intakeshaft, wherein the absorbent particles react with the sulphur compoundscontained in the flue gases extracted from the conbustlon chamberthrough the gas-intake shaft. A layer of reacted absorbent is thenformed on the surface of the absorbent particles. Because the absorbent,along with the fuel, is transported from the gas-intake shaft to thepulvenzer, this layer is destroyed and the absorbent particles are mixedwith the fuel. Subsequently, as the fuel mixed with the absorbent issupplied to the combustion chamber via the absorbent-injection ductaligned with the burner, there occurs a further interaction between theunreacted absorbent particles and the sulphur compounds.

So in this case, the absorbing agent is used twice: within thegas-intake shaft and within the combustion chamber, thereby ensuring itsessentially complete utilization and hence, high economical andenvironmental performance of the proposed furnace.

The use of flue gases for preparation and drying of a high-volatile fuelby feeding it to the gas-intake shaft and subsequent preparation of thisfuel by means of a pulverizing fan is virtually known in itself. Theauthors, however, are not familiar with furnaces wherein the absorbentis supplied to the upper region of the gas-intake shaft and used forbinding the sulphur compounds twice: first, in the gas-intake shaft, andthen within the combustion chamber.

BRIEF DESCRIPTION OF THE DRAWING

The invention is now illustrated by the accompanying drawing in which:

FIG. 1 is a schematic representation of a furnace for burning a solidorganic fuel, a sectional elevational view.

FIG. 2 is a schematic sectional elevational view of the furnace, inaccordance with another embodiment of the invention.

FIG. 3 is a schematic sectional elevational view of the furnace, inaccordance with a third enbodiment of the invention.

DESCRIPTION OF PREFERRED EMBODIMENT OF THE INVENTION

Referring now to FIG. 1, the furnace comprises a combustion chamber 1with a downwardly tilting burner 2 for supplying the air-fuel mixturemounted on its wall. The angle of the longiltudinal axis of the burner 2with a projection of this axis onto the wall is denoted by α in FIG. 1.A prism-shaped ash-hopper with a slot mouth 4 is defined by slopes 3 ofthe walls in the lower region of the combustion chamber 1. The angle ofthe slope 3 with the vertical line is denoted by β in FIG. 1. Disposedbeneath the ash hopper mouth 4, over the entire width thereof, is abottom blast device 5 used to generate a turbulent zone in the lowerregion of the combustion chamber 1. A duct 6 for injection of acalcium-bearing absorbent region of the combustion chamber 1. A duct 6for injection of a calcium-bearing absorbent such as lime or calciumcarbonate mixed with fuel is located below the burner 2. Thelongitudinal axis of the duct 6 is tilted downwardly, the angle made bythe longitudinal axis of the duct 6 with a projection of this axis ontothe wall of the combustion chamber being denoted by γ in the drawing.The absorbent-injection duct may also be disposed at the same elevationas the burner for supplying the air-fuel mixture. In both cases, theabsorbent-injection duct 6 is preferably positioned so that slope y ofthe longitudinal axis of the absorbent-injection duct 6 is no less thanthe angle β made by the slope 3 of the combustion chamber walls definingthe ash hopper and no greater than angle α made by the longitudinal axisof the burner 2. In this case, the axis of the absorbent-injection duct6 is passed through the lower region of the combustion chamber, crossingthe central portion of the turbulent zone.

FIG. 2 shows another embodiment of the invention. Referring to FIG. 2,an absorbent-injection duct 7 is disposed in the outlet nozzle of abottom blast device 8. In this case, the axis of the duct 7 runs along aslope 10 of a combustion chamber 11, crossing the lower region of thechamber and hence, the turbulent zone.

When such furnace is operated, as shown in FIG. 1, the air-fuel mixtureis supplied through the burner 2, air is introduced through the bottomblast device, and a calcium-bearing absorbent, generally, lime orcalcium carbonate mixed with fuel is supplied through theabsorbent-injection duct 6. As a result of interaction between air-fuelmixture streams, fuel-absorbent mixture and bottom blast air, two majorcombustion zones are generated in the furnace chamber, namely:parallel-flow and turbulent zones. The composition of the fuel-absorbentmixture selected is dependent on the characteristics of the fuel and theabsorbent. The fraction of the absorbent in the total mass ranges from10 to 100% and is chosen from considerations of the best possiblebinding of sulphur and the most economical expenditure of the absorbent.

Fine particles of the absorbent are ignited near the burner and burnedwithin the parallel-flow part of the flame. Simultaneously, fineparticles of the absorbent are entrained in the upgoing airstreams fromthe bottom blast device and also carried over to the parallel-flow partof the flame, wherein they interact with the fuel particles to bindsulphur.

Medium-sized and coarse particles of the fuel and absorbent areseparated into the turbulent zone. In this zone, the fuel particles areburnt out in the course of repeated recycling. Absorbent particles arerecycled in the turbulent zone along with the fuel particles. As aconsequence of a repeated recycling of the particles and a longresidence time within a zone being at a temperature most favourable interms of the sulphur-binding reaction conditions, this reaction proceedsmore vigorously. This is facilitated by a good mixing of absorbentparticles and flue gases in the turbulent zone. As the fuel particlesare recycled in the turbulent zone, they are burned out, become lighterand are carried to the parallel-flow zone and then, already as fly ashand flue gas, vented to the smoke stack. During recycling in theturbulent zone, the absorbent particles are mechanically destroyed as aresult of impacting the fuel particles and the combustion chamber walls,though still participating in the sulphur-binding reactions. The fineparticles of the absorbent that is, generally, already utilized, i.e.bound with sulphur are entrained in the upgoing streams and carried overto the parallel-flow zone of the furnace, and then to the smoke stack.

The furnace of FIG. 2 operates in a similar manner, except that bothfine and relatively coarse particles of the absorbent are received bythe turbulent zone via the duct 7. The fine particles are carried to theparallel-flow zone, whereas the coarse and medium-sized particles,similarly to the previous design are recycled within the turbulent zone,reacting with absorbing material sulphur

Referring to FIG. 3, the furnace comprises a prism-shaped combustionchamber 12 with an ash hopper 13 defined by the slopes of the walls inthe lower region of the combustion chamber, and a botton blast inletdevice 14 extending along the entire width of a slot mouth 15 of the ashhonper 13. The furnace further includes a burner 16 mounted on its walland a vertically elongated gas-intake shaft 17. The gas-intake shaft 17communicates at the top with the inner space of the combustion chamber12 through a gas-intake window 18 and a duct 19. The duct 19communicates in turn with an absorbent-feeding duct 20. The lower regionof the gas-intake shaft 17 communicates with a pulverizing fan 21 andthen, through the burner 16, with the inner space of the combustionchamber 12. The duct (not shown in the drawing) for injection of theabsorbent into the furnace chamber is aligned with the burner.

As the furnace is operated, the fuel is fed through a chute 22 to thegas-intake shaft 17. At the same time, hot flue gases are admittedthrough the gas-intake window 18 to the duct 19 and then to thegas-intake shaft 17, the flue gases being premixed with thesulphur-compound binding absorbent conveyed through the duct 20 to theduct 19. As the flue gases and the absorbent and fuel particles passalong the gas-intake shaft 17, the fuel is heated, the volatile matterreleased and mixed with the flue gases. Simultaneously, a reaction ofbinding the sulphur compounds with the absorbent proceeds on the surfaceof the absorbent particles. Since the flue gases are at a temperatureranging from 600 to 1100° C., which is known to be the most favourabletemperature range for such sulphur-binding reaction to be effective,optimum conditions for binding the sulphur compounds are ensured in thegas-intake shaft 17. The fuel mixed with gas and absorbent istransferred from the gas-intake shaft 17 to the pulverizing fan 21. Inthe pulverizing fan 21, the fuel is further dried, its particles and theparticles of the absorbent are pulverized and mixed. In the course ofthis treatment, the surface layer of the absorbent particles isdestroyed and the so-far unreacted core of these particles now becomesaccessible. Thus the absorbent particles are ready for reuse. Theprepared mixture is fed to the burner 16. The fine particles of the fueland the volatile matter burn in the vicinity of the burner, within theparallel-flow part of the flame. The coarser, solid, particles of thefuel and the absorbent go down to the lower region of the furnace andare entrained in the air stream coming from the bottom blast inlet 14and directed along the slope of the ash hopper. The opposite streams ofthe air mire from the burner and the air supplied by the bottom blastinlet device interact to generate a turbulent zone having a temperatureof about 1000° C. A repeated recycling of the fuel and absorbentparticles and the flue gases within this zone allows their longresidence at a temperature which is most effective for binding thesulphur, thereby ensuring an essentially complete utilization of theabsorbent.

Investigations made by the authors have shown that the proposed furnaceprovides a substantially reduced sulphur oxide content of the flue gasesalong with an economical use of the absorbent. In addition, such filnaceis safe to operate even if a high-volatile fuel is used. The proposedfurnace is so designed as to allow the use of the fuel and the absorbentmaterial of a relatively large-sized fraction composition, causing theexpenses involved in their preparation to be somewhat reduced.Furthermore, owing to the advantages inherent in the swirling typefiurnaces with a repeated recycling of particles in the furnace chamber,an essentially complete utilization of the absorbent is ensured,resulting in a still more cost-effective operation of the furnace.

The proposed invention can be employed in designing new furnaces as wellas in the overhaul of existing boiler units equipped with furnaces usingas fuel bituminous coals and lignites with a sulphur content of morethan 1%, as-received basis.

The proposed invention was realized in overhauling a furnace of apower-generating boiler using as fuel a coal dust with the lowestcombustion heat of 4500 to 5000 kcal/kg and a sulphur content of 1.0 to1.5%, as-received basis. The furnace includes four burners disposed eachon one of the four walls of the furnace. Each burner is designed as anarrangement of three overlying ducts. Located below each of the burnersis one duct for injection of the absorbent mixed with the fuel in theproportion of about 50% by mass. The angle made by the longitudinal axisof the upper duct of each burner with a projection of this axis onto thevertical wall of the combustion chamber was 80 deg., the angle made bythe longitudinal axis of the middle duct of each burner with aprojection of this axis onto the vertical wall of the combustion chamberwas 70 deg, and the angle made by the longitudinal axis of the lowerduct of each burner with a projection of this axis onto the verticalwall of the combustion chamber was 60 deg. The angle of the longitudinalaxis of the absorbent-injection duct with a projection of this axis ontothe vertical wall of the combustion chamber was 35 deg. The amount ofsulphur oxides vented to the atmosphere was reduced, after the overhaulby some 40 to 50%.

What is claimed is:
 1. A furnace comprising: a prism-shaded combustionchamber with an ash hopper having a slot mouth defined by sloping wallsof the combustion chamber in a lower region of the combustion chamber;at least one burner mounted on one of said walls of the combustionchamber for injecting a solid organic fuel into the combustion chamber;a duct for injecting a sulfur-absorbing material into the combustionchamber; and, a bottom blast inlet device disposed adjacent the slotmouth of the ash hopper and across an entire width of the ash hopper forgenerating a turbulent zone in lower region of the combustion chamber,the duct being located between the burner and the ash hopper and beingoriented in such a manner that a longitudinal axis defined by the ductis directed towards the turbulent zone.
 2. The furnace according toclaim 1 wherein the burner for feeding the air-fuel mixture is tilteddownwardly, the absorbent-injection duct is disposed on the same wall asthe burner, an angle γ made by the longitudinal axis of theabsorbent-injection duct with a projection of the longitudinal axis ontosaid same wall is no less than an angle β made by a sloping wall of thecombustion chamber with the vertical lying on said same wall and nogreater than an angel α made by the longitudinal axis of the burner witha projection of the longitudinal axis onto said same wall of thecombustion chamber.
 3. The furnace according to claim 1 furtherincluding an absorbent-injection duct disposed in the outlet nozzle of abottom blast device.
 4. The furnace according to claim 1 wherein thefurnace is adapted to burn said solid organic fuel as a mixture withsaid sulfur-absorbing material, where a proportion of thesulfur-absorbing material in the mixture ranges from 10% to 100% bymass.
 5. The furnace according to claim 1 further including: agas-intake shaft; a duct for feeding the sulfur-absorbing material intothe gas-intake shaft; and, a pulverizing fan communicating thesulfur-absorbing material from the duct to said at least one burner.